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Naomi Watts had some good reasons not to play Princess Diana in an upcoming biopic.

But aside from the fact that she's undoubtedly putting herself in the line of fire for her portrayal of the late royal, the one thing that definitely worried the actress was what Prince William and Prince Harry might think of her performance as their mum.

In an interview with the U.K.'s Sunday Times (via Grazia Daily), the 44-year-old Watts admitted that she almost didn't take the part out of fear of offending Diana's grown children.

"The biggest reason that made me pause was how the princes were going to be feel about this," "The Impossible" star told the Times. "There was actually quite an eerie moment in London when I did see Prince William in a restaurant, and I got very nervous, because if I caught his eye I didn't want to interpret a look and think he had a negative feeling about this idea, so I made sure not to look."

Luckily, that run-in with Wills didn't deter her from the film. "Diana" chronicles the last two years of the Princess of Wales' life and her love affair with heart surgeon Dr. Hasnat Khan ("Lost's" Naveen Andrews) before her untimely death in Aug. 1997 from injuries sustained in a car crash in Paris after being pursued by paparazzi.

"I turned it down twice," Watts told the paper about being offered the role two years ago. 'I was a little bit torn, but once I'd said no, I wasn't completely at peace. Sometimes when you say no, you feel free, but it just wasn't the case."

Naomi noted that the pull of playing Lady Di was ultimately too great however so she accepted.

"There was something very intriguing about this woman's life. It was extraordinary. She always lived a privileged life, but there was noting ordinary about the construct she moved into," said Watts. "I liked the idea that there was this fame--no one at that level can really survive it, I think. It's a very dark thing, but it's kind of true."

As for William and Harry, the A-lister added: "I do care deeply about how the princes feel, of course. I am a mum of two boys. But it was a story that was bound to be told at some point, and it's possibly fresher than people expected."

Whether or not Watts hits the mark with her performance, we'll have to wait until the first reviews are in following "Diana's" world premiere in London on Sept. 5. The flick, which is based on Kate Snell's 2001 book "Diana: Her Last Love," doesn't yet have a U.S. release date.

As one of Diana's main characters, the doctor told the Mail on Sunday that the film was "completely wrong" and that he doesn't plan to see it. He also slammed claims by "Diana's" producer that he gave the big-screen tale "tacit acceptance."

"It is a complete lie. I have never given any approval," said Khan, who's remained silent on the subject of his relationship for Diana since her passing. "It is based on gossip and Diana's friends talking about a relationship that they didn't know much about, and some of my relatives who didn't know much about it either. It is all based on hypotheses and gossip."